At the corner of two sunbaked streets in San Antonio, decorator Gwynn Griffith has created her own rich, personal refuge in a late-19th-century brick edifice that hardily withstands the Texas heat. Inside, the temperature is cool, and the rooms give new meaning to the word "collected." With great passion, Griffith has juxtaposed antique cabinets, a Pop Art "hand" chair, a French chaise longue, African stools, and Mexican plaster lions—all within walls that pulsate with color. Saturated greens. Electric blues. Even a deep tobacco-brown in the grand living room, where dozens of mercury "gazing" balls dangle from the ceiling, catching glimmers of the Texas light that cascades through windows nearly 13 feet high.

The scale of the former industrial building—which has housed, over the years, a shoe factory, a seed company, and a metalworking shop—means that there's plenty of wall and floor space for Griffith's collections of paintings, drawings, photographs, and sculptures. Some are by Griffith herself; many are the work of her sons, Sam Giesey and Greg Mannino, artists who inhabit the second and third floors of the three-story structure. "It's a family compound," says Griffith of the building, just two blocks from the San Antonio River and next door to the adobe house that was once owned by the infamous Judge Roy Bean.

The realization of this art-filled oasis didn't happen without vision and pluck. Griffith, who has run a one-woman design firm for nearly 30 years, first moved into the building as a tenant in 1994, when the metal shop on the ground floor was fully operational. "There was still ironworking going on," she says. "Bang, bang, bang!" It turned out that Griffith wasn't the only occupant of her third-floor rental space. "There were bats and pigeons. I used to hunt squab up there with a pellet gun. It was a very primitive situation." She made the best of it by raising walls, turning the open loft into a cozy haven.

Five years later, when a chance to buy the entire building presented itself, Griffith took the leap. Out went the first floor's metalworking equipment and drill presses; up went more walls. A raised concrete floor where welders once worked was chopped up and hauled away. Old French windows were modified to fit the existing openings. ("I wanted to fling them open," says the decorator. "Of course, when it rains, I have to go around and close them all. Now I know why double-hung windows were invented.")

Griffith left intact at least one remnant of the building's industrial history: the scarred pine flooring, which has been infused with character by scorch marks from a forge's flying sparks and coals. Ultimately, she moved downstairs, transforming the raw space into a combination residence and design office. (The relocation also offered easy access to the property's remarkably lush gardens, where she grows spinach, jalapeños, tomatoes, and basil.)

As Griffith applied color and brought in art and antiques, the ground floor came alive. The rich and layered palette sprung "from out of my head," she says. The entry hall glows emerald-green. The kitchen walls blend lemon and lime. The effect everywhere is theatrical—a fitting backdrop for her quirky, eclectic assemblages, hunted and gathered in shops, on trips, and online.

Griffith's mastery at mixing elements is self-taught. She planned to be a marine biologist, she says, but fell into her current career, first designing an office for her former husband, then homes for friends. She has filled her own space the same way she decorates for clients: intuitively and organically, her only design tenet being an affinity for pairs, to add a bit of order to an array of disparate pieces.

She collects energetically, with no plan or theme. "There are more Latin-flavored paintings than anything else," she says, "but it's not intentional." The work of her artist sons crops up in bursts. In the master bedroom, a mural of a Persian landscape by Mannino fills the walls, with trees stretching to the ceiling. In a cabinet in the room she calls her "chamber of curiosities," a sculpture by Giesey takes pride of place. It's a clay figure of a supine chicken, augmented with taxidermy head and feet—"a Mother's Day present," says Griffith, laughing.

Lately the decorator has found herself being pulled in new aesthetic directions. "All the rooms I've fiddled with recently I've changed to white," she says. She is drawn to modernist paintings of the 1930s and '40s, and to sleek contemporary light fixtures. There are hints of this unusual new direction at her own home: to wit, a pair of chairs by Vignelli Associates, circa 1985, which look like handkerchiefs caught in free fall. They pull up to a well-weathered, white-marble table in the kitchen. "I'm a restless spirit," confesses Griffith. "I love change. I've been known to move the bed to the middle of the living room if the mood strikes." Her eyes twinkle. "Nothing is nailed down."